How does sunscreen work?

Lobster red skin is difficult look to pull off, but sunburn and other UV damage can easily be avoided with a bit of a common sense and a good splodge of sunscreen.

What is ultraviolet radiation?

UV (ultraviolet) radiation has a shorter wavelength than visible light. Much of the energy emitted by the sun is in the form of UV, although our planet’s atmosphere – particularly the ozone layer - does a good job of filtering most of this type of radiation out before it reaches us.

Without any protection from the atmosphere, UV is a significant hazard for astronauts: if their skin was exposed they would be burnt in a matter of seconds. And even down on Earth, it makes sense to be cautious, as UV rays can cause sunburn as well as more permanent damage to your skin or eyes.

How much UV radiation you’re exposed to when out and about depends on several factors, including proximity to the equator, altitude, time of day, season and cloudiness. If you’re planning a lunchtime picnic on Mount Kilimanjaro, you’d better make sure you pick a shady spot.

UV radiation is divided into categories according to its wavelength (see above). UV-B radiation is to blame for sunburn, whilst UVAs are responsible for long term skin damage. Thankfully, sunscreen can protect us from both these invisible enemies.

Stopping UV in its tracks

Sunscreens help to filter out UV radiation using a combination of two main types of active ingredients. Inorganic particles, such as titanium dioxide or zinc oxide, form a physical barrier, reflecting or scattering UV waves. Organic components meanwhile absorb UV rays and release their energy as heat.

The light-reflecting inorganic compounds meant that early sunscreens were almost indistinguishable from white paint. Nowadays though, nanotechnology has made it possible to produce completely clear sunscreens which still fend off UV rays just as effectively. They contain the same ingredients as traditional formulations, but the inorganic particles are so small that they are invisible.